1. Field of the Invention
The present invention relates to a process for producing a xylylenediamine by a liquid-phase hydrogenation of a dicyanobenzene in the presence of a catalyst, and more particularly, to a process for producing the xylylenediamine in which the catalyst having its activity decreased in the course of the hydrogenation is regenerated for reuse in the hydrogenation of the dicyanobenzene. The xylylenediamine is useful as a raw material for production of polyamide resins, curing agents, etc., as well as an intermediate material for isocyanate resins, etc.
2. Description of the Prior Art
It is well known in the art to produce the xylylenediamine by hydrogenating dicyanobenzene in the presence of a catalyst.
For example, Japanese Patent Publication No. 38-8719 discloses an autoclave batchwise hydrogenation of a dicyanobenzene into a corresponding diamine in an alcohol solvent in the presence of a very small amount of a caustic alkali agent and Raney nickel. Japanese Patent Application Laid-Open No. 54-41804 discloses another batchwise hydrogenation of a dicyanobenzene in an autoclave. The proposed hydrogenation is conducted in a mixed solvent of a lower alcohol and a cyclic hydrocarbon in the presence of a hydroxide or alcoholate of alkali metal or alkaline earth metal, and a Raney nickel catalyst to produce the corresponding diamine. Japanese Patent Publication No. 53-20969 discloses a catalytic reduction of a dicyanobenzene with hydrogen in a liquid phase in the presence of a Ni/Cu/Mo-containing catalyst, for example, by a fixed bed continuous hydrogenation.
However, in any of the above conventional methods, the catalyst is gradually deactivated during the course of use, resulting in unsatisfactory yields of the aimed product. In addition to such a lowering of the catalytic activity, in a fixed bed reactor, the pressure drop through the catalyst layer due to adhesion of high-boiling substances makes continuous operation of the reactor difficult.
Journal of Catalysis, 143 (1993), pp. 187-200 teaches that a nickel catalyst (25% by weight of nickel on SiO2) used in a gas-phase hydrogenation of acetonitrile can be regenerated by a hydrogen treatment at 200° C. or higher.
Japanese Patent Application Laid-Open No. 2000-508305 teaches that a nickel-containing catalyst used for producing 6-aminocapronitrile and hexamethylenediamine simultaneously by hydrogenating adiponitrile can be regenerated by a hydrogen treatment at 150 to 400° C. under a hydrogen pressure of 0.1 to 30 MPa for 2 to 48 h.
Japanese Patent Application Laid-Open No. 2000-508304 discloses that a cobalt- or iron-containing catalyst used for producing an NH2-containing compound by hydrogenating a compound containing a carbon-nitrogen unsaturated bond can be regenerated by a hydrogen treatment at 150 to 400° C. under a hydrogen pressure of 0.1 to 30 MPa for 2 to 48 h. This patent document teaches that aliphatic nitrites, especially adiponitrile is preferred as the compound containing a carbon-nitrogen unsaturated bond, and discloses the regeneration of the catalyst used in the hydrogenation of adiponitrile and 3-cyano-3,5,5-trimethylcyclohexylimine in its working examples.
Japanese Patent Application Laid-Open No. 2001-526956 discloses that a Raney nickel catalyst used for the hydrogenation of nitrites can be regenerated by treating the catalyst with an aqueous solution of a basic compound having a basic ion concentration of 0.01 mol/L or higher at a temperature of lower than 130° C., and then washed with water until the pH of the washings reaches 12 to 13, exemplifying the regeneration of the catalyst used for the hydrogenation of adiponitrile.
However, the above documents are all concerned with the regeneration of the catalysts used for the hydrogenation mainly of aliphatic nitrites, and silent as to whether or not catalysts used for the hydrogenation of aromatic dinitriles such as dicyanobenzene are equally regenerated by the proposed method, and also, whether or not a pressure drop through the catalyst layer of a fixed bed reactor can be got rid of by the proposed method.